Dr. Jordan Tobin, the PI on the project retired. At present, the research questions and objectives remain the same. The goal is to characterize the age-related changes in bone mass that have been demonstrated in both men and women. Age and sex related differences hormones, nutritional and physiological variables involved in bone turnover are important in elucidating changes in bone physiology in normal aging and disease. Specifically, the relationships of age and sex to changes in body composition, both as a marker of obesity and as a measure of the weight-bearing load on bone are important factors in bone status and rates of change. The most dramatic rates of change in bone mass occur at the menopause, and changes of body composition, bone mass, and bone markers and hormones are being investigated in 114 women aged 45-55 who have been recruited to the Baltimore Longitudinal Study of Aging as part of the perimenopausal cohort. The women, who were still menstruating, on entry to the study, are followed at 3month intervals as they traverse the menopause, and for two years since their last period. These studies will allow for the interpretation of the changes that occur prior to and mmediately around the time of the cessation of menses, changes that can only be appreciated in a prospective longitudinal study. Currently, 20-30 women are continuing to be studied. Sarcopenia, the loss of muscle (lean) mass and strength with increasing age, has become an important process used to explain aspects of decreasing functional peformance in the elderly. Lean mass is typically studied using either anthropometric measurements or through imaging techniques. DXA is currently a method that allows for the assessment of body composition and bone mineral density. Body composition studies typically evaluate fat mass with an adjustment for body size using either BMI or percentage body fat while adjustments for lean mass are used less frequently. An analysis has compared two adjustments for lean mass (percent lean mass, and lean mass per height squared (lean mass index)), and provides normative values by age for DXA derived body composition measurements in Caucasian and African American men and women. African American men averaged 3.1 kg more lean mass and 1.8 kg less fat mass than Caucasian men at all ages. African American women averaged 1.6 kg more lean mass and 3.4 kg more fat mass than Caucasian women at all ages. Use of percent lean mass, and lean mass index adjust for size differences when examining lean mass across age thus facilitating comparisons of lean mass across individuals of differing height better than the direct use of lean mass. Future work will examine the degree to which physical activity, muscle strength and cardiovascular fitness alter age associated losses in muscle mass and bone density. Can changes in young to middle age adults alter these age-associated changes?